ABO3 perovskite-type metal oxides such as lead zirconate titanate (referred to as “PZT” hereinafter) are typically used as piezoelectric materials. Since PZT contains lead as the A site element, a concern has been raised over PZT's impact on the environment. Thus, piezoelectric materials that use lead-free perovskite-type metal oxides are highly desirable.
An example of a lead-free piezoelectric material that contains a perovskite-type metal oxide is barium titanate. Studies on and development of barium-titanate-based materials have been conducted to improve properties of barium titanate. PTL 1 and NPL 1 each disclose a material having a piezoelectric property improved by substituting some of A sites of barium titanate with Ca and some of B sites with Zr. However, such a material has a low Curie temperature of 80° C. or less and undergoes depolarization in a severe environment such as car compartments under summer sun, resulting in degradation of the piezoelectric property. Moreover, since the mechanical quality factor is small, the material is likely to undergo depolarization when AC voltage is applied.
PTL 2 and NPL 2 each disclose a material prepared by substituting some of A sites of barium titanate with Ca and adding Mn, Fe, or Cu. Such a material has a mechanical quality factor superior to that of barium titanate but exhibits a low piezoelectric property.